The present disclosure relates to a thermal transfer sheet onto which a dye is thermally transferred.
A thermal transfer method using a sublimation dye includes transferring a number of color dots to a thermal transfer material by heating within a very short period of time and reproducing a full-color image using various color dots. In such a thermal transfer method, an image or a character is formed by closely adhering a dye layer of a thermally transferring sheet to a thermal transfer sheet, heating the thermally transferring sheet from a reverse side of the dye layer using heating means such as a thermal head according to an image signal, and transferring a dye included in the dye layer to the thermal transfer sheet. In this case, a sheet having a dye receiving layer formed therein to receive a dye transferred from the thermally transferring sheet on a surface of a sheet-shaped base material is used as the thermal transfer sheet. According to the thermal transfer method using such a sublimation dye, a high-definition and high-density recorded matter is obtained.
In recent years, as digital cameras have come into wide use, there is an increasing demand for a thermal transfer method by which such a high-definition and high-density recorded matter can be obtained. Furthermore, there is a demand for obtaining an image having high sensitivity and excellent light fastness.
As technology satisfying the above-mentioned requirements, for example, International Publication No. WO7006/057192 discloses a thermal transfer sheet including a dye receiving layer containing a graft polymer of polyester and at least one monomer selected from an acrylic monomer and a methacrylic monomer. The characteristics of the dye receiving layer include high sensitivity and excellent light fastness.
In the technology of International Publication No. WO2006/057192, however, it is necessary for the dye receiving layer to further include an isocyanate-based curing agent in an aspect of securing heat resistance (blocking resistance). For this reason, a dye receiving layer is formed in a process of manufacturing a thermal transfer sheet by coating a base sheet such as a printing paper with a solution obtained by dissolving a resin and a curing agent in solvent as a dye receiving layer and drying the coated solution. In this case, it is necessary to install separate equipment so as to re-collect and store an evaporated solvent. Also, humidity-curing polyisocyanate is generally used as a curing agent that is added to strengthen the film strength of a dye receiving layer. When the humidity-curing curing agent is used, a solution for forming a dye receiving layer is coated and dried, and a resin is cured under the environment of uniform temperature and humidity. As a result, it may also be necessary to separately add an aging process or equipment used in the aging process. For the above-described reasons, when the curing agent is used to form the dye receiving layer as described in International Publication No. WO2006/057192, a manufacturing process is complicated, and equipment is large and specialized. As a result, the productivity is lowered, thereby resulting in an increase in manufacturing costs.
Meanwhile, for example, Japanese Patent Laid-Open Publication No. H04-101891 discloses a thermal dye transfer receiving element obtained by a method by which a resin coating layer is pressed onto a paper support. In this method, a solution for a dye transfer receiving layer is not coated onto a base as described above, but a thermoplastic resin is softened with heat and elongated using a nip roller to be laminated as a dye receiving layer on a base sheet such as a printing paper. For this reason, the method of Japanese Patent Laid-Open Publication No. H04-101891 is inexpensive compared with a coating method because a manufacturing process is simple and there is less necessity for large-scale and specialized manufacturing equipment.
Also, Japanese Patent Laid-Open Publication No. S63-319188 discloses a sublimable image-receiving material for thermal transfer recording using a copolymer resin (hereinafter also referred to as an “AS resin”) which is formed using acrylonitrile and styrene as essential ingredients, which are materials applicable to the technology described in Japanese Patent Laid-Open Publication No. H04-101891.